Conventional communications devices such as phones typically don't offer the instant communications feature with a push of a button. On a typical phone, a user needs to press several buttons to dial a phone number. Then there is the ringtone waiting for the callee to pick up the call. So the communication is not instant and it requires pushing multiple buttons. A callee is the person who receives an incoming call. On the callee's end, a callee has to push at least a button to be able to hear the caller.
Some cell phones have the push-to-talk feature that offers the instant voice with a push of button. However, push-to-talk on a cell phone is mainly designed for one-to-many type of group calls. Additionally, these push-to-talk calls are only half duplex, meaning communication is one way at any time, therefore only one party can talk at a time by seizing the floor first. There are instant messaging software systems that indicate the status of the other users and allow users to send instant messages to each other, but these systems don't provide instant voice or video services.
Additionally, a conventional phone call consists of two call legs: one call leg going from the caller to the callee and the other call leg going from the callee to the caller. Basically, both call legs have to be set up before the caller and callee can communicate. Callers and callees don't have control of the call legs separately.
In real life, a caller may only need to speak to a callee without any expectation of any response from the callee. Therefore only an outgoing call leg from the caller to the callee is needed. Similarly, a callee may only want to listen in on a call. Therefore there no need to set up a call leg from the callee to the caller. With traditional phones, there is no option for a caller or a callee to control the call legs.
Furthermore, the need for call set up on a broadband network is obviated as the network bandwidth grows. Call setup causes delay which hinders instant communications. The concept of call set up originates from the circuit switched networks where resources are scare and need to be allocated. As the voice communications evolve from circuit switched network to packet switched network, Voice over IP (VoIP) technologies were developed. VoIP also requires call setup due to the limited network resources at the time of its development. In today's wireless and fixed networks, resources are abundant relatively speaking in consideration of the bandwidth requirements of the real-time voice and video communications.